Fiber grating is a novel passive sensing element having the advantages of high sensitivity, high electromagnetic interference resistance, and corrosion resistance. After fiber grating is applied to sensing, it has experienced rapid and sustained development, and has broad application prospects in safety monitoring in the fields of aeronautics and astronautics, building construction, and oil. A fiber grating demodulation system is the key part of an entire sensing system. Fiber grating demodulation technologies are developing toward the trend of high precision, high resolution, combination of dynamic and static parameters, multi-point multiplexing detection, and low costs. There are various fiber demodulation methods. Among others, the tunable F-P filter method can only be applied to the measurement of the static strain, the tunable laser method requires high costs, and the non-equilibrium Mach-Zender interference method is susceptible to environmental impact, which is conducive for engineering application. In recent years, with the rapid development of optical detectors, small fiber spectrometers have developed rapidly, and fiber demodulation technologies based on spectral imaging also have developed.
Fiber grating demodulators based on spectral imaging have a small size and high degree of integration, and can be applied to the measurement of both static and dynamic strains. Therefore, they have prominent advantages among the demodulation methods, and are an important research direction for demodulation systems. The performance of the optical system is the key of the demodulator because the performance of the optical system directly affects the system resolution.
There are various structures for the optical system of a grating spectrometer. Currently, the Czerny-Turner light path structure is commonly used, which uses two concave reflecting mirrors as a collimating mirror and an imaging focus mirror respectively and uses a planar reflective grating as a dispersion element. One reason is that the planar grating is not difficult to design, can be produced at low costs, and has a high diffraction efficiency. Another reason is that the Czerny-Turner structure has a large number of structural parameters that can be adjusted and set, which can prevent the occurrence of two or more times of diffraction, so that a photodetector array can be used to receive the spectrum. Common small Czerny-Turner spectrometers are mainly divided into two types: crossed-type and M-type. The M-type structure is a classic Czerny-Turner spectrometer structure, and a typical product of this type is Avaspec series small fiber spectrometer developed by Avantes, Holland. The crossed-type structure is an evolution from the M-type structure, and has a more compact structure and higher spatial utilization. However, as the number of pixels in a linear array image sensor is limited, the spatial resolution of the spectrum is limited.
Therefore, a technical problem to be solved in the art is how to implement accurate wavelength demodulation of a high resolution grating in the case of the limited number of pixels in a linear array sensor.